Deriving IdentitiesDate: 08/26/98 at 09:09:06 From: Marie McLean Subject: Deriving Identities Hi, I hope you can help me with a problem I can't seem to figure out. I'm supposed to derive the identity for sin 3x in terms of sin x. I was told to use the identity for sin(a+b) on sin(2x + x) as a first step. I tried that and I was able to get further but I keep doing something wrong. I would appreciate any help. Date: 08/26/98 at 11:30:14 From: Doctor Rick Subject: Re: Deriving Identities Hi, Marie - How far were you able to get? How do you know you did something wrong - do you know what the answer should be? If so, it's possible your answer is correct but that you need to apply a trig identity to get it in the form you expect. If you write the formula for sin(2x + x) and substitute the formulas for sin(2x) and cos(2x) where the latter appear in the formula, you should get an expression that has sin(x) and cos(x). You can eliminate the cos(x) and get it in a nice form by using cos^2(x) = 1 - sin^2(x). - Doctor Rick, The Math Forum http://mathforum.org/dr.math/ |
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